Question about dealership diagnostic fee for CEL

Assuming gas cap has always been on, and tightened to one click, my money is on DTC P1121 (3 way coolant control valve). The CEL (Check Engine Light) is intermittent. Sometimes it stays on for days/hours/minutes, then will disapper, then will reappear after days/hours/minutes, and the cycle continues. No change in car's performance, engine sound, exhaust sound. There may be other problems that could duplicate this as well.

Get it read for free at Midas, Autozone, etc. Call around to see what parts stores and repair shops off free OBD2 code reading. This is the cheapest work around. However, these places use a generic OBD2 reader that can't read all of the Prius codes.

Even if you don't DIY, best to do yourself a favor and buy miniVCI off Amazon/eBay for $25. This will give you the same diagnostic capability as dealers, as they use the same cable (granted a genuine cable vs knock off imitation) and software (legitimate vs a hacked copy). This being said, many here have been using the hacked stuff off Amazon/eBay w/o any problems, doing maintenance and reading codes! You can now read the codes w/ accuracy (generic readers miss a lot of codes and give false codes) at your convenience, and cheaply ($25 vs $115).

Click this LINK, and choose any mini VCI cable; I'd get the cheapest one (new or used). You can always find a newer software version of Techstream somewhere on the Internet.

READ ME FIRST link. The Tundra boys provide an easy ABC, 123, for mini VCI. You should have no further questions after reading this. There is even a link w/in this article for a 64bit Window's set-up.

Hardware Requirements link, by Toyota, just note the speed and RAM requirement for your soon to be Techstream laptop.

To be data safe, assume the hacked Techstream software has malware. This laptop should be a spare "junker," used only for Toyota diagnosis/maintenance; NO email, NO online banking, NO nothing where a user ID and password is ever entered.
Some people have reported success using a Mac laptop in some Windows XP emulation mode.

EDIT.
If the valve is stuck in the wrong position, you may not have cabin heat and/or the engine will take a longer time to warm-up.

If you are in a CARB state, you might be able to get this replaced under the emissions warranty free of charge. This assumes you are still under 150K miles, as you are obviously under 10 years w/ your 2009 Prius.

 

sounds like the dealer is being up front with you. good advice above from ex and mac.

 

It could be P1121. Until you get the code read, you won't know for sure. Call other auto store chains and repair shops near you. Call another AutoZone.

As stated above, if the valve is stuck in the wrong position, you may not have cabin heat and/or the engine will take longer to warm-up. If it is the 3-way valve, the question becomes how long can you function w/o heat? On cold winter days, heat and A/C are important to help keep the front windshield defrosted. You could also pull out a towel/rag to wipe the windshield, as the poor man's defroster.

Really invest in miniVCI and a junker-laptop. You won't be wondering or at the mercy of free code read. $25 vs $115; assuming free laptop. You probably have friend's who know someone in IT, who has obsolete laptops lying around. You'll be able to use this device on other Toyotas; newer models probably will require the latest version of TechStream that may/many not be available as a hacked copy.

As for warranty, look at the warranty booklet for your model year; it is possible Toyota could change the terms/duration from model year to model year. I got mine covered under the Emissions Warranty in California. However, other PC members in California did not have the same luck. It seems some dealers will fix it under warranty, others won't.

EDIT:
B/C I had mini VCI, I saw P1121. Went to dealership saying P1121, should be covered under the longer Emissions Warranty. Received a phone call later in the afternoon, repair completed, under warranty. Its possible this same dealer could have said NO too. However, knowing ahead of time what caused the CEL (Check Engine Light) may have helped?